Step 1Heat the oven to 350 degrees. Spread the walnuts on a baking sheet and toast them in the oven until they are browned and fragrant, about 15 minutes. Set aside.
Step 2In a medium bowl, combine the eggs, egg yolk, oil and wine; set aside. In a large bowl, stir together the sugar, flour and salt, and sift in the baking powder. Stir to combine, then slowly add the egg mixture. Stir until smooth. Fold in the walnuts.
Step 3Pour the batter into a buttered and floured 9-inch cake pan. Bake for about 35 to 40 minutes or until a toothpick inserted into the center comes out clean. Cool on a rack, then carefully transfer to a serving plate or cake stand.
Step 4To make the glaze, split the vanilla bean in half lengthwise and scrape out the beans with the back of a knife. Discard the bean pod. In a small saucepan, combine the sherry, powdered sugar and vanilla bean seeds. Heat over medium heat just until the sugar is dissolved. Strain.
Step 5Prick small holes in the top of the cake with a fork. Pour warm glaze over the cake. Sprinkle with sifted powdered sugar.